1. Field of the Invention
This invention relates to a rechargeable nickel-zinc battery wherein a combination of electrochemical elements is composed of a sheet-like negative electrode containing zinc compound as the active material, a sheet-like positive electrode containing nickel oxide compound as an active material, a separator, an electrolyte absorber and an alkaline electrolyte.
2. Description of the Prior Art
Recently, many experiments have been carried out in an attempt to develop rechargeable batteries having alkaline electrolyte and zinc compound used as a negative electrode material, because such a combination would have many excellent characteristics such as high energy density, high working voltage, reasonable material cost, excellent heavy drain duty performance and low temperature duty characteristics. After many technological efforts improvements to obtain a long life for charge-discharge cyclic operations have been found. An electrode, for an example, was made by coating a mixture of zinc oxide and/or zinc powder and mercury or mercuric oxide on a current collector wherein the zinc oxide and/or zinc powder comprised from 80 to 90 wt % of the mixture and the mercury or mercuric oxide comprised 5 to 20 wt %. However, the discharge capacity of the battery having this electrode gradually decreases if the battery is subjected to a repetitive charge-discharge operation even under the low current density of 2 to 3 mA/cm.sup.2. In such an operation it was difficult to go over 50 cycles as the capacity decreased to half the initial capacity. The rechargeable batteries in commercial use muse keep more than half of the initial capacity even after the 200th charging treatment. To produce such batteries, new improvements in the zinc electrode, the positive electrode, the separator, the electrolyte absorber and the electrolyte are necessary.
A good rechargeability for a battery can be expected, if the discharged product of the zinc electrode of the battery does not dissolve into the electrolyte during discharge. One electrode tested for preventing the dissolution was a sheet-like zinc electrode containing calcium hydroxide for fixing the discharge products as CaZn(OH).sub. 4 on the electrode as reported by N. A. Zhulidov in U.S.S.R. Author's Certificate No. 116812 filed on Mar. 7, 1958. However, this electrode cannot endure high drain discharge service because of the formation of passive film on the zinc powder which is called passivation phenomena. Also, a semi-dry-type negative electrode in which the amount of the electrolyte was restricted in order to prevent the dissolution of the reactive products into the electrolyte was tested but it, too, proved unsatisfactory. Accordingly, there is a need for a battery capable of undergoing many charge-discharge cycles at a high drain rate of discharge.